Rio 2016 day one: Australia bags gold in women relay

Australia's Emma McKeon, Brittany Elmslie, Cate Campbell and Bronte Campbell, from left, celebrate their gold medals after winning the women's 4x100-meter freestyle relay final setting a new world record during the swimming competitions at the 2016 Summ 

Hungary's Katinka Hosszu celebrates winning a gold medal in the women's 400-meter individual medley during the swimming competitions at the 2016 Summer Olympics, Saturday, Aug. 6, 2016, in Rio de Janeiro, Brazil. | AP

Australia's Cate Campbell, Bronte Campbell, Emma McKeon and Brittany Elmslie, from left, hold their gold medals after winning the women's 4x100-meter freestyle final setting a new world record during the swimming competitions at the 2016 Summer Olympics

Australia's Cate Campbell starts her final leg of the 4 x 100m freestyle championship final swimming competition ahead of USA's Katie Ledecky at the 2016 Summer Olympics, Saturday, Aug. 6, 2016, in Rio de Janeiro, Brazil. | AP

Hungary's Katinka Hosszu celebrates after setting a new world record and winning the gold medal in the women's 400-meter individual medley final during the swimming competitions at the 2016 Summer Olympics, Saturday, Aug. 6, 2016, in Rio de Janeiro, Bra

United States' Kevin Cordes competes in a semifinal of the men's 100-meter breaststroke during the swimming competitions at the 2016 Summer Olympics, Saturday, Aug. 6, 2016, in Rio de Janeiro, Brazil. | AP

Australia's Cate Campbell, is greeted by teammates after anchoring the team to gold in the women's 4x100-meter freestyle relay as United States' Katie Ledecky looks on during the swimming competitions at the 2016 Summer Olympics, Saturday, Aug. 6, 2016

Australia's Emma McKeon, Brittany Elmslie, Bronte Campbell and Cate Campbell celebrate after winning the gold medal and setting a new world record in the women's 4x100-meter freestyle final during the swimming competitions at the 2016 Summer Olympics, S